In Firefox Merging Two Cells of a Table Does not Work

Problem

While using Confluence in firefox, merging two cells of a table does not work. While merging 3 cells is possible. Also selecting 3 cells and marking two and then merging works.

Environment

1. Any Confluence version
2. Firefox browser 72.0.1
.

Steps to Reproduce

1. Edit a Confluence page and include a table containing several rows and columns.
2. Select two cells and then use the "merge" icon at the top the merge the two cells.
3. Select three cells then use the "merge" icon at the top the merge the two cells.
4. Select three cells, but reduce selection to two and then use the merge icon.

Expected Results

For all steps 2,3 & 4 the cells should be merged.

Actual Results

1. For step 2, cells are not merging.
2. For step 3 cells are merging.
3. For step 4, cells are merging.

Workaround

Workaround is to use Chrome or IE. 

Notes